1. Field of the Invention
The present invention relates generally to the field of bolts and other threaded fasteners, and more specifically to a locking bolt assembly, which extends above a surface to an adjustable extent and which is lockingly inserted into an aperture in a base member fastened to the surface, the aperture having a central segment and a countersunk segment, including a tubular outer bolt portion having external threads at a first end for screwing into the threaded countersunk segment of the aperture and having an axial bore, and an inner bolt portion in the form of a shaft having external threads at a first end oriented opposite to the threads on the outer bolt portion and being of greater length than the outer bolt portion, for inserting through the axial bore of the outer bolt portion and engaging opposite threads in the central segment of the aperture beyond the counterbore, and having a head at its second end for abutting and creating a friction engagement with the second end of the outer bolt portion, thereby binding and locking the outer and inner bolt portions together against rotation in either direction.
2. Description of the Prior Art
There have long been fastening structures having internally threaded tubular portions for performing spacing and securing functions. These structures generally have either not been of adjustable protruding distance or have not been lockingly securable.
One such prior structure is that of Burke, U.S. Pat. No. 4,295,765, issued on Oct. 20, 1981. Burke teaches a tie-down structure which fits into a hole in the bed of a truck, the hole being surrounded by a downwardly beveled rim portion. A body member is provided having an externally threaded stem portion, a beveled rim portion and an axial bore with an internal thread. The stem portion is fit downward through the hole and the beveled flange portion abuts the beveled rim of the hole. An annular positioning member fits over the stem portion from underneath the bed and has a beveled recess to fit snugly against the beveled rim area around the hole. The positioning member helps center the body portion and secure it against lateral movement. A nut fits over the stem portion and against the positioning member to fasten the structure in place. Then an eye bolt is screwed into the axial bore. A problem with Burke if used as a spacing bolt is that no provision is made to extend the bolt to various distances and to lock the bolt in place at those distances.
Farrington, U.S. Pat. No. 824,983, issued on Jul. 3, 1906, discloses a double screw assembly having an externally threaded outer body portion for screwing into a surface. The body portion has a point at one end for penetrating the surface and a threaded axial bore in the other end for receiving a conventional machine screw. The body portion provides a permanent anchor in which the machine screw can be removably inserted. A problem with Farrington if used as a spacing bolt is that no means is provided for locking the machine screw at varying insertion depths, to leave various shank lengths protruding.
Brosseit, U.S. Pat. No. 3,461,769, Aug. 19, 1969, reveals an adjustable length shoulder screw. An internally threaded tube having an external flange at one end is inserted through a hole in a first work piece until the flange abuts the rim of the hole. A coil spring is placed around the protruding end of the tube and the protruding end is placed over a threaded hole in a second work piece. A threaded rod, having an Allen wrench socket in one end, is screwed into the tube and partially into the threaded hole in the second work piece. The coil spring enhances friction between the threaded rod and the tube and the threaded hole, to prevent the rod from working loose. A problem with Brosseit is that it is apparently useful only for joining two work pieces. It is not suited for providing a locking spacing bolt of adjustable extension length.
Rosan, U.S. Pat. No. 2,823,574, issued on Feb. 18, 1958, discloses a self-tapping fastener. The fastener has a self-tapping end with threads of slightly reduced outside diameter, and a subsequent series of threads of slightly larger diameter, so that their tips have a predetermined interference fit with the screw thread cut by the self-tapping end. A replacement fastener is provided with at least one additional screw thread arranged for an interference fit to restrain the replacement fastener against accidental loosening. A problem with Rosan is that the use of the fastener is limited to surfaces made of materials which lend themselves to self-tapping. Another problem is that once the fastener is in place, it cannot be re-adjusted to a lesser depth without becoming loose.
Zaydel, U.S. Pat. No. 4,186,645, issued on Feb. 5, 1980, teaches a plastic plug, nut and stud fastener assembly for securing a first member to an apertured second member. An externally threaded tubular plug is inserted through the aperture until an external radial flange on the plug abuts the aperture rim. A nut is screwed over the tubular plug to secure it in the aperture. Then an end of a stud having a centrally located radial flange is pressed into the tubular plug, the interior of plug being splined to increase gripping friction. The other end of the stud beyond the flange, which is externally threaded, is fastened into a hole in the second member. A problem with Zaydel is that the extent of second end projection from the first member is not readily adjustable after installation.
It is thus an object of the present invention to provide a spacing bolt assembly which can be secured to most surfaces and protrudes to an adjustable distance.
It is another object of the present invention to provide such an assembly which can be locked into position when the protrusion distance is selected.
It is still another object of the present invention to provide such an assembly which can be unlocked and readjusted to a new protrusion distance with conventional wrenches.
It is finally an object of the present invention to provide such an assembly which is sturdy, reliable and relatively inexpensive to manufacture.